A review on covalent organic frameworks: exploration of their growing potential as porous materials in photocatalytic applications

Photocatalysis powered by unlimited solar energy is an effective strategy to resolve energy and environmental issues. To achieve an efficient photocatalytic system, photocatalysts need to be highly crystalline and porous with excellent photostability under extreme conditions. In this case, covalent organic frameworks (COFs) have shown immense potential for photocatalytic applications owing to their unique structure as well as electronic and photophysical characteristics. COFs possess a crystalline porous network with light absorption capabilities and excellent stability. Furthermore, functionalized COFs can be developed through organic unit variation to obtain broader absorption, narrow bandgap, effective charge separation, and transportation. Furthermore, high photocatalytic efficiency can be achieved via the formation of heterostructures through anchoring or post-synthetic modification. Our review is focused on the recent advancements in COFs as photocatalysts for various photocatalytic applications. Initially, we emphasize the topological design, linkage chemistry, and functionalization of COFs, underscoring the principles and requirements for high photocatalytic efficiency. This provides deep insights into the capabilities of COFs in different photocatalytic applications, covering areas such as hydrogen and oxygen evolution, carbon dioxide reduction, organic transformation, and organic pollutant degradation. Finally, we summarize the pivotal points that need urgent attention and outline future avenues, offering fresh perspectives and contributing to revolutionary innovations in this rapidly evolving field. This review explores advancements in COFs for photocatalytic applications, focusing on mechanisms enhancing COFs' synergy, identifying research gaps in design strategies and key factors, and suggesting new directions for future research.